The present invention relates to a method of electronic brake force distribution.
Electronic brake force distribution is used to prevent the rear wheels from locking prior to the front wheels. When needed, the brake pressure of the rear wheels is therefore maintained by corresponding switch actuation or even decreased in the further procedure to prevent still further increase of an increased brake slip, or to decrease the brake slip. Vehicles with a front-axle/rear-axle brake circuit allotment typically include a pressure switch in the front-axle brake circuit. The purpose of the switch is to prevent, upon brake circuit failure on the front axle, an electronic brake force distribution on the rear axle from allowing a too low deceleration of the vehicle during braking. This is because there is a standard which demands at least 30% vehicle deceleration upon failure of a brake circuit. As a rule, a pressure switch is closed in the absence of front-axle brake pressure. Electronic brake force distribution is then only possible when the pressure switch is open because this indicates a pressure increase in the front-axle brake circuit. Irrespective of the exact function of the pressure switch, electronic brake force distribution will be deactivated in any case when a defective front-axle brake circuit is identified.
However, monitoring the front-axle brake pressure is not possible when the pressure switch suffers from a malfunction. This means that the electronic controller in the vehicle does not know whether or not appropriate front-axle brake pressure is built up, i.e., whether or not electronic brake force distribution is possible. Either only the pressure switch could be defective and the front-axle brake circuit intact, or a so-called double failure could have occurred, meaning that the front-axle brake circuit has failed and the pressure switch is defective.
An object of the present invention is to provide a method of electronic brake force distribution which contributes to increasing the vehicle stability even when the pressure switch is defective.